In a communication system, it is often required to perform switch among data channels for high-speed data transmission. Generally, the switch is performed via a multiplexer-demultiplexer (MUX-DEMUX). The MUX-DEMUX includes a passive switch. Stray capacitance and limited on-resistance in the passive switch may cause attenuation to a signal passing through the passive switch, and the attenuation is severe for a signal with a high frequency. Therefore, a technical problem to be solved by those skilled in the art is how to solve the attenuation to the signal caused by a switch circuit.